Polyphosphonates are known to exhibit excellent fire resistance (see e.g., U.S. Pat. Nos. 2,682,522 and 4,331,614). It is known (see e.g., U.S. Pat. No. 2,682,522) that linear polyphosphonates can be produced by melt condensing a phosphonic acid diaryl ester and a bisphenol using a metal catalyst (e.g., sodium phenolate) at high temperature. This approach produced low molecular weight polyphosphonates that exhibited poor toughness.
Consequently, to improve toughness a synthetic approach to produce branched polyphosphonates by the transesterification process was developed (see e.g., U.S. Pat. No. 4,331,614). This approach involved the transesterification reaction of a phosphonic acid diaryl ester, a bisphenol, a branching agent (tri or tetra phenol or phosphonic acid ester), and a preferred catalyst (e.g., sodium phenolate) carried out in the melt, usually in an autoclave. Several patents have addressed the use of branching agents in polyphosphonates (see e.g., U.S. Pat. Nos. 2,716,101; 3,326,852; 4,328,174; 4,331,614; 4,374,971; 4,415,719; 5,216,113; 5,334,692; and 4,374,971). These approaches have met with some degree of success, however, the combination of properties exhibited by these polyphosphonates are still not sufficient for general acceptance in the marketplace. For example in branched polyphosphonates, the number average molecular weights as high as 200,000 g/mole are claimed with a minimum requirement of 11,000 g/mole (see e.g., U.S. Pat. No. 4,331,614) with polymer dispersities less than 2.5. Consequently these polyphosphonates exhibited high melt viscosities. This approach was successful in producing high molecular weight polyphosphonates that exhibited improved toughness, but processability was sacrificed.
Both linear and branched polyphosphonates produced by the transesterification process exhibited excellent flame resistance, however they generally lack hydrolytic stability and can be degraded by moisture. All polyphosphonates prepared to date are amorphous thermoplastic materials that are not known to crystallize (e.g., form ordered morphological structures). Crystallinity in organic polymers is known to impart some advantageous properties including higher heat distortation temperatures, higher thermal stability and improved solvent and moisture resistance. The ability to crystallize a polymer or prepolymer into a powder form offers several additional advantages. These include enabling additional reactions or operations that can be performed in the solid state such as subsequent reactions to increase the molecular weight or dry mixing with other polymer powders. Performing these steps in the solid state avoids the difficulty of handling high viscosity melt polymerization or melt mixing operations that require specialized equipment, are difficult and expensive.